JP2009290206A - Pupil filter for aligner, diffractive optical element and aligner provided therewith - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a pupil filter that can prevent an amount of light passing through the pupil filter used in illumination optical systems for semiconductor optical aligner or the like from being reduced, can reduce load for correction of optical proximity effects without dimensional variation of an image pattern on a wafer depending on the mask pattern pitch, and can obtain a stable high resolution optical image. <P>SOLUTION: The pupil filter 1 includes an optical transmission part 11, an optical shield part 13, and a low optical transmission region 12. The pupil filter 1 includes a low optical transmission region 12 disposed at the center region thereof, with a transmittance lower than that of the optical transmission part 11 but higher than that of the optical shield part 13, a circular optical transmission part 11 coaxially disposed at the outer circumference of the optical transmittance region, and a circular light shield part 13 coaxially disposed at the outer circumference of the light transmission part 11. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a pupil filter, a diffractive optical element, and an exposure apparatus provided with the same used in a projection exposure apparatus used for pattern formation of semiconductor elements and the like.

  In order to form a circuit pattern of a semiconductor element or the like, a process generally called a photolithography technique is required. In this step, usually, a method of transferring a photomask (also referred to as a reticle; hereinafter simply referred to as a mask) pattern onto an exposed substrate such as a semiconductor wafer is employed. A photosensitive photoresist is applied on the substrate to be exposed, and a circuit pattern is transferred to the photoresist in accordance with the pattern shape of the mask pattern. In the projection exposure apparatus, the image of the circuit pattern to be transferred drawn on the mask is projected and exposed on the substrate to be exposed (wafer) via the projection optical system.

  In photolithography technology, the minimum dimension (resolution) that can be transferred by a projection exposure apparatus is proportional to the wavelength of light used for exposure and inversely proportional to the numerical aperture (NA) of the projection optical system. With the demand for the reduction in wavelength, the exposure light has been shortened and the projection optical system has a higher NA. However, there is a limit to satisfying this requirement only by the shorter wavelength and the higher NA.

  Therefore, in order to increase the resolution, a super-resolution technique for reducing the size by reducing the value of the process constant k1 (k1 = resolution line width × the numerical aperture of the projection optical system / the wavelength of the exposure light) has been recently proposed. Yes. As such a super-resolution technique, a mask pattern is optimized by giving an auxiliary pattern or line width offset to the mask pattern according to the characteristics of the exposure optical system, or a modified illumination method (oblique illumination method, multipole illumination). And so on). In the modified illumination method, usually, annular illumination using a pupil filter, dipole (also referred to as dipole or dipole) illumination, quadrupole (also referred to as quadrupole or quadrupole) illumination, or the like is used. ing.

  FIG. 9 is a schematic configuration diagram of an exposure system of a semiconductor projection exposure apparatus. A light source 91 such as an ArF excimer laser and a pupil filter 92 are arranged as modified illumination means. An illumination light 93 is a lens 97 of the projection optical system. Then, an image is formed on the wafer 98 of the substrate to be exposed. The “pupil filter” here is a pupil filter of the illumination optical system, and is disposed on the condenser lens 94 on the mask 95.

  FIG. 10 is a schematic top view showing an example of the shape of a conventional pupil filter. The shaded portion indicates the light transmitting portion with respect to the light transmitting portion, and the light transmittance is 1% or less, and the non-hatched portion indicates the light. A transmission part is shown. FIG. 10A shows a normal pupil filter, in which most of the circular pupil includes a light transmitting portion 101 that transmits light emitted from a light source, and a peripheral portion is a light shielding portion 102. FIG. 10B shows an example of the shape of a pupil filter for modified illumination. The central portion is shielded as a light shielding portion 104, and two fan-shaped light transmission portions 103 are provided at symmetrical positions in the center of the pupil filter.

  In the case of a general circular pupil filter as shown in FIG. 10A, the diffraction angle (t) of the diffracted light from the mask is determined by the mask pattern pitch (d) and the light wavelength (L). It is represented by the following formula (where n is the diffraction order). Therefore, when a specific light source is used, the diffraction angle (t) of the diffracted light varies depending on the pitch of the mask pattern.

sin (t) = n × L / d
FIG. 11 is an explanatory diagram showing the relationship between the pitch of the mask pattern and the diffracted light of the illumination light after passing through the pupil filter.

  FIG. 11A shows a case where the pattern pitch of the mask 115a is large with respect to the exposure wavelength, and the illumination light 113a forms an image on the wafer surface and a good image is obtained. However, with the miniaturization of semiconductor elements, the mask pattern pitch is becoming smaller and smaller. FIG. 11B shows a case where the pattern pitch of the mask 115b is small with respect to the exposure wavelength, and the illumination light 113b no longer forms an image on the wafer surface, and a good image cannot be obtained. FIG. 10C shows a case where light is incident obliquely under the same conditions as in FIG. 11B (oblique incidence illumination method), and the illumination light 113c can be imaged on the wafer. As described above, with the miniaturization of the semiconductor element, the pitch of the mask pattern is also reduced, and an oblique incidence exposure method has been used.

  In order to realize the oblique incidence illumination method shown in FIG. 11C, the pupil shape of the pupil filter is changed from, for example, the conventional circular pupil shown in FIG. 10A to the dipole shown in FIG. If the fan-shaped pupil is used, the central part of the pupil filter is shielded to allow oblique component light to be incident, thereby improving the resolving power.

  However, by changing the pupil filter for illumination from FIG. 10 (a) to FIG. 10 (b), the following new problems have arisen.

  First, as a first problem, when the pupil filter shown in FIG. 10B is realized by an aperture (generally, metal plate processing), the amount of illumination light transmitted through the pupil filter of FIG. 10B is reduced. As a result, the exposure time becomes longer, the efficiency of semiconductor exposure becomes very poor, and the semiconductor manufacturing cost increases. For this reason, use of a diffractive optical element has been proposed in order to reduce the loss of the light amount (see, for example, Patent Document 1 and Patent Document 2).

  Next, since the pupil filter of FIG. 10B has a smaller area through which illumination light is transmitted than the pupil filter of FIG. 10A, the light emitted from the pupil filter is very coherent. The following second problem has occurred.

  FIG. 12 is a schematic top view of a pattern showing the pitch of the mask pattern. The black portion is a light shielding portion with a light transmittance of 0.1% or less with respect to the light transmitting portion, and FIG. 12A shows a small pitch. FIG. 12B shows the case where the pitch is large. FIG. 13 shows the contrast when (Imax−Imin) / (Imax + Imin) is the contrast, where the horizontal axis represents the mask pattern pitch, the vertical axis represents the maximum light intensity Imax, and the minimum light intensity is Imin. It is shown and it is a figure explaining the relationship between the pitch of a mask pattern, and the coherence of the illumination light which radiate | emits a pupil filter. Curve (a) in FIG. 13 is a circular pupil, and curve (b) in FIG. 13 is a fan-shaped pupil.

  When the mask pattern pitch becomes smaller on the mask and becomes 200 nm or less on the wafer surface, as shown by the curve (a) in FIG. 13, in normal illumination using a circular pupil, the contrast rapidly decreases and the resolution decreases. . However, the contrast is stable when the pitch is large and the wafer surface is 300 nm or more.

  On the other hand, as shown in the curve (b) of FIG. 13, in the modified illumination using the fan-shaped pupil, the mask pattern pitch is reduced, and the contrast is kept high up to about 120 nm on the wafer surface. However, when the pattern pitch changes, the contrast changes regularly and the contrast is not stable. This means that the pattern size imaged on the wafer varies depending on the mask pattern pitch. To correct this variation, a powerful correction technique such as optical proximity correction (OPC) is used. Is required. However, since the coherence of the illumination light emitted from the pupil filter is high, the range in which this OPC must be applied is widened, resulting in a problem that data processing becomes a heavy burden and OPC correction becomes difficult. .

JP 2001-174615 A JP 2005-243953 A

  The present invention has been made in view of the above problems. In other words, it is possible to prevent a reduction in the amount of illumination light transmitted through a pupil filter used in an illumination optical system such as a semiconductor exposure apparatus, and to reduce the load when performing correction by the optical proximity effect. The present invention provides a pupil filter, a diffractive optical element, and an exposure apparatus including the same that can obtain a stable and high-resolution optical image without changing the size of an image pattern.

  The present invention solves the above-described problem, and irradiates a mask with light emitted from a light source via an illumination optical system, and projects a pattern on the mask onto an exposure substrate via a projection optical system. In the pupil filter used in the illumination optical system of the exposure apparatus, the pupil filter includes a light transmissive portion, a light shielding portion, and a low light transmittance region, and has a lower transmittance than the light transmissive portion at the center, The light low transmittance region having a higher transmittance than the light shielding portion is disposed, the annular light transmission portion is disposed concentrically on the outer periphery of the light low transmittance region, and concentric on the outer periphery of the light transmission portion. The annular light-shielding portion is disposed in the upper portion.

  The transmittance of the low light transmittance region is in the range of 5% to 30%.

  When the diameter of the pupil filter is 1, the dimensional ratio in the radial direction of the low light transmittance region is 0.8, the dimensional ratio in the radial direction of the light transmitting portion is 0.1, and the light shielding The dimensional ratio of the portion in the radial direction is 0.1.

  According to the present invention, it is possible to prevent a reduction in the amount of illumination light transmitted through a pupil filter used in an illumination optical system such as a semiconductor exposure apparatus, and to reduce the load when performing correction by the optical proximity effect, and to reduce the mask pattern pitch. As a result, the pattern size imaged on the wafer does not fluctuate, and a comprehensive and stable high-resolution optical image can be obtained.

It is a figure which shows the pupil filter which concerns on this invention. It is a figure which shows the general pupil filter used conventionally. It is a figure which shows the relationship between the pitch on a mask, and the contrast on a wafer. It is the figure which expanded a part of FIG. It is a figure which shows the relationship between a pitch and the minimum decomposition dimension (CD). It is a figure which shows the relationship between a pitch and an OPC bias. It is an enlarged front photograph figure which shows the example of the computer generated hologram element of this invention. An example in which illumination light is incident on the computer generated hologram element of the present invention to form a dipole fan-shaped pupil filter is shown. It is a schematic structure schematic diagram of an exposure system of a projection exposure apparatus for semiconductor. It is an upper surface schematic diagram which shows the example of a shape of the conventional pupil filter. It is explanatory drawing which shows the relationship between the pitch of a mask pattern, and the diffracted light of the illumination light after passing a pupil filter. It is an upper surface schematic diagram of the pattern which shows the pitch of a mask pattern. FIG. 5 is a diagram illustrating the relationship between the mask pattern pitch on the horizontal axis and the contrast of the optical image on the vertical axis, and the mask pattern pitch and the coherence of illumination light emitted from the pupil filter.

  Hereinafter, embodiments of the pupil filter of the present invention will be described with reference to the drawings. FIG. 1 is a diagram showing an embodiment of a pupil filter of the present invention.

  As shown in FIG. 1, the pupil filter 1 of the present embodiment includes a light transmission portion 11 and a low light transmittance region 12. The low light transmittance region 12 has a circular shape arranged at the center of the pupil filter, and the transmittance is set lower than that of the light transmitting portion arranged at the outer periphery. The light transmission portion 11 is formed of a concentric ring arranged on the outer periphery of the low light transmittance region 12 and preferably has a transmittance of 100%. Further, the outside of the light transmission part 11 and the low light transmittance region 12 includes a light shielding part 13 concentric with the light transmission part 11 and the low light transmittance region 12.

  Reference numeral 121 denotes a radial dimension of the low light transmittance region, 122 denotes a radial dimension of the low light transmission part, and 123 denotes a radial dimension of the light shielding part.

  FIG. 1A shows the transmittance of the low light transmittance region 12 as 5%, and FIG. 1B shows the transmittance of the low light transmittance region 12 as 10%. FIG. 1C shows a case where the transmittance of the low light transmittance region 12 is 20%, and FIG. 1D shows a case where the transmittance of the low light transmittance region 12 is 30%.

  Next, comparative evaluation between the conventional pupil filters A, C5 and C9 and the pupil filter 1 of the present invention will be described. The evaluation standard uses contrast stability and resolving power.

  As a general pupil filter used as a comparison target, one having a structure as shown in FIG. 2 is used.

  FIG. 2A shows a first conventional pupil filter C5 having a light transmission part 11 at the center and a light shielding part 13 on the outer side. In the first conventional pupil filter C5 used in the present embodiment, the ratio of the radial dimension of the light transmission part 11 is 0.5 when the whole is 1.

  FIG. 2B shows a second conventional pupil filter C9 having a light transmission part 11 at the center and a light shielding part 13 on the outer side. In the second conventional pupil filter C9 used in the present embodiment, the ratio of the dimension in the radial direction of the light transmission part 11 is 0.9 when the whole is 1.

  FIG. 2C shows an annular pupil filter A having a light shielding part 13 at the center, a light transmitting part 11 on the outer periphery thereof, and a light shielding part 13 on the outer side thereof. In the annular pupil filter A used in the present embodiment, the ratio of the dimension in the radial direction of the central light shielding part 13 is 0.8 when the whole is 1, and the light transmitting part 11 on the outer periphery thereof is in the radial direction. Between 0.8 and 0.9.

  First, the contrast of the pupil filter 1 having the low light transmittance region 12 at the center according to the present invention and the general pupil filters A, C5, and C9 were compared.

  3 and 4 are diagrams showing the relationship between the pitch on the mask and the contrast on the wafer. FIG. 3 shows the contrast up to a pitch of 800 nm. FIG. 4 shows a contrast up to a pitch of 300 nm, and is an enlarged view of a part of FIG.

  As shown in FIGS. 3 and 4, the first conventional pupil filter C5 has a contrast of 0.9 or higher when the pitch is large and is stable in a high state. However, in the region where the pitch is about 200 nm or less, the first conventional pupil filter C5 is abrupt. The contrast decreases.

  The second conventional pupil filter C9 has a lower contrast than the first conventional pupil filter C5 in a region where the pitch is about 200 nm or more, but is stable at 0.7 to 0.8.

  When the pitch is about 200 nm or more on the wafer surface, the annular pupil filter A has a contrast of about 0.6, which is lower than the first conventional pupil filter C5 and the second conventional pupil filter C9. However, when the pitch is about 200 nm or less, the change is small, and the contrast is high as compared with the first conventional pupil filter C5 and the second conventional pupil filter C9, and good characteristics are shown.

  The pupil filter 1 having the low light transmittance region 12 in the center according to the present invention has a contrast of 3% to 10% higher than that of the annular pupil filter A at a pitch as large as 250 nm on the wafer surface, and at a pitch as small as 150 nm on the wafer surface. The contrast is 10% to 100% higher than the first conventional pupil filter C5 and the second conventional pupil filter C9. That is, a stable contrast can be obtained for all pitches.

  Next, the resolutions of the pupil filter 1 having the low light transmittance region 12 in the center according to the present invention and the general pupil filters A, C5, and C9 were compared.

  FIG. 5 is a diagram showing the relationship between the pitch and the minimum resolution dimension (CD). As shown in FIG. 5, the first conventional pupil filter C5 and the second conventional pupil filter C9 have a minimum resolution dimension (CD) larger than those of the pupil filter 1 and the annular pupil filter A, and are not so good even if the pitch is changed. .

  The annular pupil filter A has a minimum resolution dimension (CD) smaller than those of the first conventional pupil filter C5 and the second conventional pupil filter C9, and becomes better when the pitch is increased.

  The pupil filter 1 having the low light transmittance region 12 in the center according to the present invention has a minimum resolution dimension (CD) smaller than those of the first conventional pupil filter C5 and the second conventional pupil filter C9, and is better when the pitch is increased. It becomes. In addition, when the transmittance of the light low transmittance region 12 at the center is increased, it becomes better.

  FIG. 6 is a diagram illustrating the relationship between the pitch and the OPC bias. As shown in FIG. 6, the first conventional pupil filter C5 is stable near the bias 0. The second conventional pupil filter C9 is unstable because of a large negative bias, irregular up-and-down fluctuation.

  In the annular pupil filter A, vertical fluctuation is observed, and the OPC bias is not stable.

  The pupil filter 1 having the low light transmittance region 12 at the center according to the present invention has a stable OPC bias and a small correction load. Moreover, if the transmittance of the light low transmittance region 12 in the central portion is increased, the stability is further improved and improved.

  As described above, the pupil filter 1 having the low light transmittance region 12 in the center according to the present invention can prevent a reduction in the amount of transmitted light and can reduce a correction load due to the optical proximity effect when generating mask pattern data. A comprehensively stable optical image can be obtained without changing the pattern size stored on the wafer depending on the pattern pitch.

  In addition, the light emitted from the light source is irradiated on the mask via the illumination optical system, and is used in the illumination optical system of the exposure apparatus that projects and exposes the pattern on the mask onto the substrate to be exposed via the projection optical system. As an embodiment of the present invention, the intensity distribution of the diffracted illumination pattern is formed so that a low diffraction efficiency region having a low intensity distribution exists at the center, and concentrically around the outer periphery of the low diffraction efficiency region. Alternatively, a diffractive optical element that arranges the high diffraction efficiency region may be used.

  In that case, it is preferable that the intensity distribution of the illumination pattern diffracted by the low diffraction efficiency portion region is in the range of 5 to 30%.

  Further, when the diameter of the illumination pattern that has passed through the diffractive optical element is 1, the dimensional ratio of the illumination pattern diffracted by the low diffraction efficiency region is 0.8, which is diffracted by the high diffraction efficiency region. The dimensional ratio in the radial direction of the illumination pattern is preferably 0.1, and the dimensional ratio in the radial direction of the non-diffractive part is preferably 0.1.

  FIG. 7 is an enlarged top view photograph showing an example of a computer generated hologram element manufactured by processing synthetic quartz. The pattern shape of the computer generated hologram element shown in FIG. 7 can be obtained by optimization using iterative calculation by a computer. FIG. 7 shows a case where the output angle (α) and pitch as a computer generated hologram element are changed, and a case where a computer generated hologram element in the case of two stages, four stages, and eight values is created by changing the number of etching stages. Yes. In FIG. 7, the collection efficiency of illumination light in the case of 2, 4, and 8 stages is 45%, 80%, and 90%, respectively.

  Therefore, if the four-stage or eight-stage hologram element of the present invention is used as the diffractive optical element for forming the pupil filter in the illumination optical system of the exposure apparatus, the light collection efficiency is as high as 80% or more and stable. A pupil filter from which a high-resolution optical image is obtained can be obtained.

  FIG. 8 is an explanatory diagram in the case where the hologram element shown in FIG. 7 is used and the illumination light is irradiated using an ArF excimer laser having a wavelength of 193 nm. The light beam incident on the computer generated hologram element 81 is diffracted by being subjected to amplitude modulation or phase modulation by the computer generated hologram element 81, and is diffracted by the computer generated hologram element 81 at a fixed emission angle α (for example, α = 3.5 °, 4.0 °). , 5.0 °) and a pupil filter having a dipole fan-shaped light transmitting portion having a desired illuminance distribution at a certain distance (220 mm when α = 3.5 ° in the example of FIG. 8) 82 (pupil outer diameter σo = 27/2 mm) is shown (only the light transmitting portion of the pupil filter 82 is shown in FIG. 8, and other portions are omitted). Here, the positions where the computer generated hologram element 81 and the pupil filter 82 are formed are arranged so as to have a Fourier transform plane relationship with each other.

(Exposure equipment)
An exposure apparatus of the present invention is an exposure apparatus that irradiates a mask with light emitted from a light source via an illumination optical system, and projects and exposes a pattern on the mask onto a substrate to be exposed via a projection optical system. The diffractive optical element for forming a pupil filter according to the present invention is provided.

  If the diffractive optical element for forming a pupil filter of the present invention can be used, various types of exposure apparatuses can be used. For example, an ArF excimer laser with a wavelength of 193 nm, a KrF excimer laser with a wavelength of 248 nm, or the like is used as an exposure light source.

  As described above, the pupil filter, the diffractive optical element, and the exposure apparatus including the same according to the present invention have been described based on the embodiments. However, the present invention is not limited to these embodiments, and various modifications can be made.

DESCRIPTION OF SYMBOLS 1 ... Pupil filter 11 ... Light transmission part 12 ... Light-low-transmittance area | region 13 ... Light-shielding part A ... Annual pupil filter C5 ... 1st conventional pupil filter C9 ... 2nd conventional pupil filter 81 ... Computer generated hologram element 82 ... Pupil filter 91 ... Light source 92 ... Pupil filter 93 ... Illumination light 94 ... Condenser lens 95 ... Mask 97 ... Projection optical system lens 98 ... Wafer 101 ... Light transmission unit 102 ... Light transmission unit 103 ... Light transmission unit 104 ... Light transmission unit 113 ... Illumination light 115 ... Mask 121 ... Radial dimension 122 of the low light transmittance region ... Radial dimension 123 of the low light transmission part ... Radial direction of the light shielding part

Claims (8)

Irradiate the mask with light emitted from the light source via the illumination optical system,
In a pupil filter used in the illumination optical system of an exposure apparatus that projects and exposes a pattern on the mask onto a substrate to be exposed through a projection optical system,
The pupil filter includes a light transmission part, a light shielding part, and a low light transmittance region,
The light low transmittance region having a transmittance lower than that of the light transmitting portion and higher than that of the light shielding portion is disposed in the central portion,
On the outer periphery of the low light transmittance region, the concentric annular light transmitting portion is disposed,
A pupil filter for an exposure apparatus, wherein the annular light shielding part is arranged concentrically on the outer periphery of the light transmitting part.   2. The pupil filter for an exposure apparatus according to claim 1, wherein the transmittance of the low light transmittance region is in a range of 5% to 30%.   3. The pupil filter for an exposure apparatus according to claim 1, wherein the light shielding portion has a transmittance of 1% or less.   When the diameter of the pupil filter is 1, the size ratio in the radial direction of the low light transmittance region is 0.8, the size ratio in the radial direction of the light transmission portion is 0.1, and 4. The pupil filter for an exposure apparatus according to claim 1, wherein a dimensional ratio in the radial direction is 0.1. Irradiate the mask with light emitted from the light source via the illumination optical system,
In the diffractive optical element used in the illumination optical system of the exposure apparatus that projects and exposes the pattern on the mask onto the substrate to be exposed through the projection optical system,
The intensity distribution of the illumination pattern diffracted by the diffractive optical element is
There is a low diffraction efficiency region with low intensity distribution in the center,
A diffractive optical element, wherein an annular high diffraction efficiency region is concentrically disposed on an outer periphery of the low diffraction efficiency portion region.   6. The diffractive optical element according to claim 5, wherein the intensity distribution of the illumination pattern diffracted by the low diffraction efficiency portion region is in the range of 5 to 30%.   When the diameter of the illumination pattern that has passed through the diffractive optical element is 1, the size ratio in the radial direction of the illumination pattern diffracted by the low diffraction efficiency region is 0.8 and is diffracted by the high diffraction efficiency region. 7. The diffractive optical element according to claim 5, wherein a dimensional ratio in the radial direction of the illumination pattern is 0.1, and a dimensional ratio in the radial direction of the non-diffractive portion is 0.1. An exposure apparatus that irradiates a mask with light emitted from a light source via an illumination optical system, and projects and exposes a pattern on the mask onto a substrate to be exposed via a projection optical system,
An exposure apparatus comprising the diffractive optical element according to any one of claims 5 to 7.

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